Investigations have continued toward obtaining information regarding regional lymph nodes (RLNs) in tumor-bearing animals with the hope that the findings will help formulate better antitumor therapeutic regimens. During the past year information was obtained regarding the optimal dosage, route, frequency and sequence of administration of a chemotherapeutic agent (Cyclophosphamide, CY) in combination with an immunostimulating agent (C. parvum, CP) necessary to produce maximal regression of tumors in our modal system. Following the receipt of such information, the in vitro cytotoxicity by lymph node cells from treated animals was evaluated. The weekly administration of CY resulted in a cyclic pattern of cytotoxicity by RLNCs. In vitro cytotoxicity of RLNCs increased 4 days after CY and by 7 days approximated that of non-treated tumor-bearing mice. CP alone had little effect on the cytotoxicity of RLNCs. The addition of CP to CY resulted in a greater cytotoxicity of cells throughout the cycle. Additional investigations have evaluated the relationship of RLNCs in tumor-bearing mice to the production of bone marrow macrophage colony forming cells (CFC) and to the cytotoxicity of the resulting macrophages. The effects of other agents such as cortisone and rifampin on LNC cytotoxicity have been evaluated. Recent investigations have been directed toward evaluating their effect on the production and cytotoxicity of macrophages by BMCs. Aside from continuing efforts to identify the relative importance of component cells of RLNs in relation to host response to a tumor and how they are affected by various therapies, investigations will be carried out to determine whether in the presence of a tumor RLNs initiate alterations in BMCs leading to increased production and cytotoxicity of macrophages, or whether the latter cells are the precursors of the changes noted in RLNs. BIBLIOGRAPHIC REFERENCES: Results of Investigations with C. Parvum in an Experimental Animal System. Fisher, B., Wolmark, N., Fisher, E.R. in Corynebacterium Parvum-Applications in Experimental and Clinical Oncology, Ed. Bernard Halpern. New York, Plenum Press, 1975. Studies Concerning the Regional Lymph Node in Cancer: VIII. Effect of Two Asynchronous Tumor Foci on Lymph Node Cell Cytotoxicity. Fisher, B. (Text Truncated - Exceeds Capacity)